Biomedical Engineering Reference
In-Depth Information
provides multiple functions to assist with body homeostasis and needs replacement
systems when confronted with organ failures such as fulminant hepatic failure (FHF).
Reports of liver treatment date back to the 1950s when low-protein diets were recom-
mended to improve mental impairment and hepatic encephalopathy, and in the 1960s novel
concepts of liver assist devices began to emerge. Some of these precedent artificial assist
systems (Artif-S) currently remain on the research bench or have entered into preliminary
FDA trials due to their intrinsic capabilities of treating patients suffering from FHF or other
liver-specific malfunctions. A few of these systems include charcoal filters for ammonia
detoxification, mechanical dialysis permitting toxin transfers, and plasmapheresis for
removal of diseased circulating substances. Investigations have shown that many Artif-S
are successful in their focused purpose, but they are not complete solutions to replace organ
function. Although Artif-S are continually being improved, the multitude of tasks per-
formed by the healthy in vivo liver continues to be insufficiently replicated through
mechanical mimics of liver cell function.
One successful hurdle in the treatment of patients with FHF is the process of tissue trans-
plantation. This technique exchanges a nonfunctioning liver with a healthy organ capable of
performing all metabolic reactions. In this way, successful replacement surgeries alleviate
the burden of using mechanical devices in concert with cellular activity. The drawback
is that patients must remain on potent immunosuppressants to lessen tissue rejection
responses, which decreases quality of life. Even though transplantation options are success-
ful, the limited supply of donor liver organs along with tissue matching requirements illus-
trate the demand is approximately 300 percent greater than the supply Ultimately, an
alternative to bridge or dissolve the
gap for patients expiring while on liver donor
lists must be resolved. This is a clear opportunity for the field of tissue engineering to
improve the standard of care and quality of life of a patient population.
waiting
6.7 CONCLUSIONS
This chapter outlined some of the key challenges and potential solutions in the field of
tissue engineering. To successfully understand tissue function, it must be possible to quan-
titatively describe the underlying cellular fate processes. Such understanding will allow the
tissue engineering to design and control these processes. One aspect of this approach is
designing the physicochemical rate processes so they match the requirements of the cellular
processes that underlie tissue function. Tissue engineering is an effort that is still in an
embryonic stage, but the use of order-of-magnitude and dimensional analysis is proving
to be valuable in designing and reconstituting tissue function.
6.8 EXERCISES
1. Given the following data, assess whether human hematopoietic stem cells can truly self-
renew in vivo:
￿ About 400 billion mature hematopoietic cells are produced daily.
Continued
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